Alarm system

From Model Year '91 all Porsche vehicles will be fitted with a new alarm system. This is a diagnosis-compatible, processor-controlled system which integrates the functions of central locking, interior light delay and an anti-theft feature.

The alarm control unit is identical for all '91 Porsche vehlcles.

Alarm Seat 964

The alarm control unit is located beneath the right-hand seat, with a cover (seat removed)


Alarm control unit with cover removed


The basic functions are for the most part the same as in the old alarm system.

For easier comprehension, the description is divided up into the following functional units:

- Function of alarm system

- Switching off alarm system

- System readiness indication

- Alarm triggering

- Type of alarm

- Anti-theft feature

- Faults

- Central locking

- Interior light delay

- Diagnosis

- Country coding

- Connecting additional systems

- Connector assignment

- Block diagram

Function of the alarm system

With the ignition key removed, the alarm can be activated in two ways.

1. Locking one of the door locks which also simultaneously operates the central locking (passive activation).

2. Locking one of the door locks rapidly three times in succession (active activation).

"Active activation" allows the alarm system to be switched on even if the central locking is faulty. The alarm control unit requires 3 activating impulses to recognize that the alarm system is to be activated despite a door that cannot be locked.

After activation of the alarm, all triggering circuits (alarm contacts) are checked to ensure that they are in proper working order. If no fault is recognized, this is indicated by rapid flashing of the LED's in the locking knobs for approx. 10 seconds (self-test).

After 10 seconds all alarm circuits are activated. The LED's in the locking knobs indicate this by slow flashing.

If a fault is recognized during the check (e.g. engine hood open, switch defective etc.), no confirmation takes place by means of rapid flashing of the LED's on the central locking knobs. After the 10 seconds, only the fault-free triggering circuits are activated. The LED's in the central locking knobs indicate this by double flashing.

If the recognized fault is eliminated (e.g. engine hood is closed), the triggering circuit concerned is activated after a 10 second delay. The LED's in the central locking knobs indicate this by slow flashing. A triggering circuit is activated if it is in its basic position for at least ten seconds without interruption.

If an alarm has been set off, this is indicated by double flashing until the alarm is deactivated.

If the tailgate is unlocked while the alarm is on, then the alarm will be deactivated. 10 seconds after the tailgate has been reclosed, the alarm system is automatically reactivated.

To prevent unintended switching on of the alarm, the speedometer signal as well as terminal 15 and terminal 61 is evaluated.

Switching off the alarm system

Switching off the alarm system, when it is activated, is performed by unlocking one of the door locks.

During the off-time (time for self-testing and input testing) of 10 seconds after activation of the system, the latter can be deactivated by switching on the ignition (terminal 15).

An alarm which has been triggered is switched off as soon as the system is deactivated.

If the tailgate is uniocked or opened while the alarm system is activated, the entire system is deactivated.

When the tailgate is reclosed, the alarm system is reactivated. System readiness indication

The operational condition is indicated by the LED's in the locking knobs of the doors. Four types of display are possible:

- No flashing (dark)

- Double flashing

No flashing

As long as the LED's do not flash, the alarm system is not in a state of readiness.

Possible reasons are:

- The system has not been switched on.

- Self-testing and input checking (10 second off-time) is not yet completed. (Self-testing has recognized a fault and reliable operation is not ensured).

Slow flashing (0.5 Hz)

When the system has been activated and is in proper working order, this in indicated by slow flashing. Prerequisites for this are:

- The system has been activated by one-time locking of one of the door locks (passive activation).

- The doors have been securely locked by the central locking.

- Self-testing revealed no fault.

- During self-testing all inputs registered open-circuit level.

- The alarm has not been triggered.

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